Anoxic/oxic membrane bioreactor assisted by electrocoagulation for the treatment of azo-dye containing wastewater

Abstract

Abstract This study investigated the use of an anoxic-oxic electro-membrane bioreactor (A/O-EMBR) for the treatment of an azo-dye containing wastewater. The reactor performance and the bacterial community structure were assessed and compared without (Period I) and with (Period II) the application of the electrocoagulation process under the current density of 10\xa0A\xa0m−2. The dye removal performance was substantially improved as the electrocoagulation was applied, increasing from 52% (Period I) to 94.9% (Period II). Respirometric tests showed that the nitrifying activity increased when the membrane bioreactor was exposed to electrocoagulation. Likewise, activity batch tests indicated that both anoxic and anaerobic dye removal rates increased when the electrocoagulation was applied, while aerobic decolorization was not affected and remained invariant. DNA sequencing analysis revealed significant shifts in the microbial community composition upon implementation of electrocoagulation. Janibacter and Lactococcus genus, recognized as azo dye-degrading bacteria, were the most abundant in Period II and accounted for almost 60% and 16% of the classified sequences, respectively. Filtration batch tests revealed better filterability conditions of the mixed liquor when the reactor was assisted by the electrocoagulation. However, the membrane fouling rate became more intense in this period, a result that was attributed to the substantial increment in total suspended solids content. The average energy consumption per mass of dye removed decreased by 17.2% (from 580 to 480\xa0kWh kgdyeremoved−1) when the electrocoagulation was applied, indicating that A/O-EMBR configuration was able to achieve a better energy efficiency in terms of dye removal.